Googler and AOSP gatekeeper Jean-Baptiste Queru announced that the factory restore images for the GSM flavored Samsung Galaxy Nexus are now available for download on the Android Building Google group this afternoon. This means that no matter how bad you screw up the system software on your new Nexus phone, you now have a path to go back to where you started, namely Android 4.0.1 (ITL41D) as well as the original baseband and bootloader. To use these images, you'll need to have fastboot up and running and have a bit of know-how about how exactly to use it, so be sure to spend a bit of time reading if you're not familiar with the process. You can find the image, with a handy flash-all script to simplify the process included, at the link below.
Source: Android Building Google group